Flexible method for producing oil bases and middle distillates with hydroisomerization-conversion followed by catalytic dewaxing

ABSTRACT

For producing very high quality base stock and for simultaneously producing high quality middle distillates, successive hydroisomerisation and catalytic dewaxmg steps are employed wherein the hydroisomerisation is carried out in the presence of a catalyst containing at least one noble metal deposited on an amorphous acidic support, the dispersion of the metal being 20%-100%. The support is preferably an amorphous silica-alumina. Catalytic dewaxing is carried out in the presence of a catalyst containing at least one hydrodehydrogenating element (group VIII) and at least one molecular sieve selected from ZBM-30, EU-2 and EU-11.

The present invention relates to an improved process for producing veryhigh quality base stock, i.e., with a high viscosity index (VI), goodstability to UV and a low pour point, from hydrocarbon feeds (preferablyfrom hydrocarbon feeds from the Fischer-Tropsch process or fromhydrocracking residues), optionally with simultaneous production of veryhigh quality middle distillates (in particular gas oils and kerosine,),i.e., with a low pour point and a high cetane index.

PRIOR ART

High quality lubricants are fundamentally important to proper operationof modem machines, automobiles and trucks.

Such lubricants are usually obtained by a succession of refining stepswhich can improve the properties of a petroleum cut. In particular,treating heavy petroleum fractions with high linear or slightly branchedparaffin contents is necessary to obtain good quality base stock in thebest possible yields, using an operation aimed at eliminating linear orvery slightly branched paraffins from feeds which are then used as basestock.

High molecular weight paraffins which are linear or very slightlybranched which are present in the oils result in high pour points andthus in coagulation for low temperature applications. In order to reducethe pour points, said linear paraffins, which are not or are only veryslightly branched, must be completely or partially eliminated.

A further means is catalytic treatment in the presence or absence ofhydrogen and because of their form selectivity, zeolites are among themost widely used catalysts.

Zeolite-based catalysts such as ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23,ZSM-35 and ZSM-38 have been described for use in such processes.

All catalysts currently used in hydroisomerisation are bifunctional,combining an acid function with a hydrogenating function. The acidfunction is provided by supports with large surface areas (in general150 to 180 m²/g) with a superficial acidity, such as halogenatedaluminas (chlorinated or fluorinated in particular),phosphorus-containing aluminas, combinations of oxides of boron andaluminium, amorphous silica-aluminas and aluminosilicates. Thehydrogenating function is provided either by one or more metals fromgroup VIII of the periodic table such as iron, cobalt, nickel,ruthenium, rhodium, palladium, osmium, iridium and platinum, or bycombining at least one group VI metal such as chromium, molybdenum ortungsten and at least one group VIII metal.

The balance between the two functions, acid and hydrogenating, is thefundamental parameter which governs the activity and selectivity of thecatalyst. A weak acid function and a strong hydrogenating functionproduces catalysts with low activity which are selective as regardsisomerisation, while a strong acid function and a weak hydrogenatingfunction produces catalysts which are highly active and selective asregards cracking. A third possibility is to use a strong acid functionand a strong hydrogenating function to obtain a highly active catalystwhich is also highly selective as regards isomerisation. Thus by carefulchoice of each of the functions, the activity/selectivity balance of thecatalyst can be adjusted.

In the process of the invention the Applicant proposes jointly producingvery good quality middle distillates, base stock with a VI and a pourpoint at least equal to those obtained with a hydrorefining and/orhydrocracking process.

SUBJECT MATTER OF THE INVENTION

The Applicant's research has been concentrated on developing an improvedprocess for producing very high quality lubricating oils and highquality middle distillates from hydrocarbon feeds, preferably fromhydrocarbon feeds from the Fischer-Tropsch process or from hydrocrackingresidues.

The present invention thus relates to a sequence of processes for jointproduction of very high quality base stock and very high quality middledistillates (in particular gas oils) from petroleum cuts. The oilsobtained have a high viscosity index (VI), low volatility, good UVstability and a low pour point.

More precisely, the invention provides a process for producing oils froma hydrocarbon feed (of which at least 20% by volume preferably has aboiling point of at least 340° C.), said process comprising thefollowing steps in succession:

-   -   (a) converting the feed with simultaneous hydroisomerisation of        at least a portion of the n-paraffins of the feed, said feed        having a sulphur content of less than 1000 ppm by weight, a        nitrogen content of less than 200 ppm by weight, a metals        content of less than 50 ppm by weight, an oxygen content of at        most 0.2% by weight, said step being carried out at a        temperature of 200-500° C., at a pressure of 2-25 MPa, with a        space velocity of 0.1-10 h⁻¹, in the presence of hydrogen, at a        ratio generally in the range 100-2000 liters of hydrogen/l of        feed, and in the presence of a catalyst containing at least one        noble metal deposited on an amorphous acidic support, the        dispersion of the noble metal being less than 20%;    -   (b) catalytic dewaxing of at least a portion of the effluent        from step a), carried out at a temperature of 200-500° C., at a        pressure of 1-25 MPa, with an hourly space velocity of 0.05-50        h⁻¹, in the presence of 50-2000 liters of hydrogen/litre of        effluent entering step b)), and in the presence of a catalyst        comprising at least one hydrodehydrogenating element and at        least one molecular sieve selected from ZBM-30, EU-2 and EU-11        zeolites.

Thus step a) is optionally preceded by a hydrotreatment step generallycarried out at a temperature of 200-450° C., at a pressure of 2 to 25MPa, at a space velocity of 0.1-6 h⁻¹, in the presence of hydrogen in ahydrogen/hydrocarbon volume ratio of 100-2000 l/l, and in the presenceof an amorphous catalyst comprising at least one group VIII metal and atleast one group VIB metal.

All of the effluent from step a) can be sent to step b).

Step a) is optionally followed by separating the light gases from theeffluent obtained at the end of step a).

Preferably, the effluent from the conversion-hydroisomerisationtreatment a) undergoes a distillation step (preferably atmospheric) toseparate compounds with a boiling point of less than 340° C. (gas,gasoline, kerosine, gas oil) from products with an initial boiling pointof more than at least 340° C. and which form the residue. Thus ingeneral, at least one middle distillate fraction with a pour point of atmost −20° C. and a cetane index of at least 50 is separated.

Catalytic dewaxing step b) is thus applicable to at least the residuefrom the distillation step, which contains compounds with a boilingpoint of more than at least 340° C. In a further implementation of theinvention, the effluent from step a) is not distilled before carryingout step b). At most, at least a portion of the light gases areseparated (by flash) and it then undergoes catalytic dewaxing.

Preferably, step b) is carried out using a catalyst containing at leastone molecular sieve wherein the microporous system has at least oneprincipal channel type with a pore opening containing 9 or 10 T atoms, Tbeing selected from the group formed by Si/Al, P, B, Ti, Fe, Ga,alternating with an equal number of oxygen atoms, the distance betweentwo accessible pore openings containing 9 or 10 T atoms being equal to0.75 mm at most.

Advantageously, the effluent from the dewaxing treatment undergoes adistillation step advantageously comprising atmospheric distillation andvacuum distillation so as to separate at least one oil fraction with aboiling point of more than at least 340° C. It usually has a pour pointof less than −10° C., and a VI of more than 95, with a viscosity of atleast 3 cSt (i.e., 3 mm²/s) at 100° C. This distillation step isessential when there is no distillation step between steps a) and b).

Advantageously, the effluent from the dewaxing treatment, which hasoptionally been distilled, undergoes a hydrofinishing treatment.

DETAILED DESCRIPTION OF THE INVENTION

The process of the invention comprises the following steps:

The Feed

The hydrocarbon feed from which the high quality oils and optionalmiddle distillates are produced contains at least 20% by volume ofcompounds boiling above 340° C., preferably at least 350° C. andadvantageously at least 380° C. This does not mean that the boilingpoint is 380° C. and higher, but 380° C. or higher.

The feed contains n-paraffins. Preferably, the feed is an effluent froma Fischer-Tropsch unit. A wide variety of feeds can be treated using theprocess.

The feed can, for example, also be a vacuum distillate from straight runcrude distillation or from conversion units such as FCC, a coker or fromvisbreaking, or from aromatic compound extraction units, or originatingfrom AR (atmospheric residue) and/or VR (vacuum residues) or the feedcan be a deasphalted oil, or a hydrocracking residue, for example fromVD, or any mixture of the feeds cited above. The above list is notlimiting.

In general, suitable feeds have an initial boiling point of more than atleast 340° C., preferably more than at least 370° C.

The feed introduced into conversion-hydroisomerisation step a) must beclean. The term “clean feed” means feeds in which the sulphur content isless than 1000 ppm by weight, preferably less than 500 ppm by weight,more preferably less than 300 ppm by weight or still more preferablyless than 100 ppm by weight. The nitrogen content is less than 200 ppmby weight, preferably less than 100 ppm by weight, more preferably lessthan 50 ppm by weight. The metal content in the feed, such as nickel orvanadium, is extremely reduced, i.e., less than 50 ppm by weight, moreadvantageously less than 10 ppm by weight, or preferably less than 2 ppmby weight.

When the amounts of unsaturated or oxygen-containing products can causetoo great a deactivation of the catalytic system, the feed (for examplefrom the Fischer-Tropsch process) must undergo hydrotreatment in ahydrotreatment zone before entering the hydroisomerisation zone.Hydrogen is reacted with the feed in contact with a hydrotreatmentcatalyst the role of which is to reduce the amount of unsaturated andoxygen-containing hydrocarbon molecules (produced, for example, duringthe Fischer-Tropsch process).

The oxygen content is then reduced to at most 0.2% by weight.

When the feed to be treated is not clean in the sense defined above, itfirst undergoes a prior hydrotreatment step during which it is broughtinto contact, in the presence of hydrogen, with at least one catalystcomprising an amorphous support and at least one metal with ahydrodehydrogenating function ensured, for example, by at least onegroup VIB and at least one group VIII element, at a temperature in therange 200° C. to 450° C., preferably 250° C.-450° C., advantageously330-450° C. or 360-420° C., at a pressure in the range 5 to 25 MPa andpreferably less than 20 MPa, preferably in the range 5 to 20 MPa, thespace velocity being in the range 0.1 to 6 h⁻¹, preferably 0.3-3 h⁻¹,and the quantity of hydrogen introduced being such that thehydrogen/hydrocarbon volume ratio is in the range 100 to 2000liters/litre.

The support is generally based on (and preferably is essentiallyconstituted by) amorphous alumina or silica-alumina; it can alsocomprise boron oxide, magnesia, zirconia, titanium oxide or acombination of these oxides. The hydro-dehydrogenating function ispreferably fulfilled by at least one metal or compound of a metal fromgroups VIII and VIB, preferably selected from molybdenum, tungsten,nickel and cobalt.

This catalyst can advantageously contain phosphorus; this compound isknown in the prior art to have two advantages for hydrotreatmentcatalysts: facility of preparation in particular when impregnating withnickel and molybdenum solutions, and better hydrogenation activity.

Preferred catalysts are NiMo and/or NiW on alumina catalysts, as well asNiMo and/or NiW on alumina catalysts doped with at least one elementselected from the group formed by phosphorus, boron, silicon andfluorine, or NiMo and/or NiW on silica-alumina catalysts, or onsilica-alumina-titanium oxide doped or not doped with at least oneelement selected from the group formed by phosphorus, boron, fluorineand silicon atoms.

The total concentration of oxides of group VIB and VIII metals is in therange 5% to 40% by weight, preferably in the range 7% to 30%, and theweight ratio, expressed as the metal oxide, of the group VI metal (ormetals) to the group VIII metal (or metals) is preferably in the range20 to 1.25, more preferably in the range 10 to 2. The concentration ofphosphorus oxide P₂O₅ is less than 15% by weight, preferably less than10% by weight.

Before being sent to step (a), intermediate separation of water (H₂O),H₂S and NH₃ can if necessary be carried out on the product obtained atthe end of the hydrotreatment step to bring the water, H₂S and NH₃contents to values of less than at most 100 ppm, 200 ppm, 50 ppmrespectively in the feed introduced into step (a). At this point, theproducts with a boiling point of less than 340° C. can optionally beseparated in order to treat only a residue in step a).

When a hydrocracking residue is treated, the feed which is present hasalready undergone a hydrotreatment and a hydrocracking step. The feedproper can then be directly treated in step a).

In general, hydrocracking takes place on a zeolitic catalyst usuallybased on a Y zeolite, in particular dealuminated Y zeolites.

The catalyst also contains at least one non noble group VIII metal andat least one group VIB metal.

Step a): Hydroisomerisation-conversion

The Catalyst

Step a) takes place in the presence of hydrogen and in the presence of abifunctional catalyst comprising an amorphous acidic support,(preferably an amorphous silica-alumina) and a metallichydrodehydrogenating function ensured by at least one noble metal. Thedispersion of the noble metal is 20%-100%.

The support is termed amorphous, i.e., free of molecular sieve, and inparticular of zeolite, as well as the catalyst. The amorphous acidicsupport is advantageously an amorphous silica-alumina but other supportscan be used. When it is a silica-alumina, the catalyst generallycontains no added halogen, apart from that which could be introduced byimpregnation, for example with the noble metal.

During this step the n-paraffins, in the presence of a bifunctionalcatalyst, undergo isomerisation then possibly hydrocracking to resultrespectively in the formation of isoparaffins and cracking productswhich are lighter than gas oils and kerosine. The conversion isgenerally between 5% and 90%, but is generally at least 20% or more than20%.

In one preferred implementation of the invention, a catalyst comprisinga particular silica-alumina is used which can produce highly activecatalysts which are also very selective for isomerising feeds such asthose defined above.

A preferred catalyst comprises (and is preferably essentiallyconstituted by) 0.05-10% by weight of at least one noble group VIIImetal deposited on an amorphous silica-alumina support (which preferablycontains 5-70% by weight of silica), with a BET specific surface area of100-500 m²/g and the catalyst has:

-   a mean mesopore diameter in the range 1-12 nm;-   a pore volume of pores with a diameter in the range between the mean    diameter as defined above reduced by 3 nm and the mean diameter as    defined above increased by 3 nm that is more than 40% of the total    pore volume;-   a noble metal dispersion in the range 20%-100%;-   a coefficient of distribution of the noble metal of more than 0.1.

In more detail, the catalyst characteristics are as follows:

Silica content: The preferred support used to produce the catalystdescribed in the present patent is composed of silica SiO₂ and aluminaAl₂O₃. The silica content of the support, expressed as a percentage byweight, is generally in the range 1% to 95%, advantageously in the range5% to 95%, more preferably in the range 10% to 80% and still morepreferably in the range 20% to 70%, or even 22% to 45%. This silicacontent can be accurately measured using X ray fluorescence.

Nature of noble metal: For this particular type of reaction, themetallic function is provided by a noble metal from group VIII of theperiodic table, more particularly platinum and/or palladium.

Noble metal content: The noble metal content, expressed as the % byweight of metal with respect to the catalyst, is in the range 0.05% to10%, more preferably in the range 0.1% to 5%.

Noble metal dispersion: The dispersion, representing the fraction ofmetal accessible to the reactant with respect to the total quantity ofthe metal of the catalyst, can be measured by H₂/O₂ titration, forexample. The metal is first reduced, i.e., it undergoes a treatment in astream of hydrogen at a high temperature under conditions such that allof the platinum atoms which are accessible to hydrogen are transformedinto the metal form. Then a stream of oxygen is passed under operatingconditions which are such that all of the reduced platinum atomsaccessible to the oxygen are oxidised to the PtO₂ form. By calculatingthe difference between the quantity of oxygen introduced and thequantity of oxygen leaving, the quantity of oxygen consumed can bedetermined. This latter value can be used to deduce the quantity ofplatinum which is accessible to the oxygen. The dispersion is then equalto the ratio of the quantity of platinum accessible to oxygen over thetotal quantity of platinum of the catalyst. In our case, the dispersionin the range 20% to 100%, preferably in the range 30% to 100%.

Distribution of noble metal: The noble metal distribution represents thedistribution of the metal inside the catalyst grain, the metal beingwell or poorly dispersed. Thus it is possible to obtain platinum whichis poorly distributed (for example detected in a crown the thickness ofwhich is substantially less than the grain radius) but well dispersed,i.e., all of the platinum atoms situated in the crown are accessible tothe reactants. In our case, the platinum distribution is good, i.e., theplatinum profile, measured using a Castaing microprobe method, has adistribution coefficient of more than 0.1, preferably more than 0.2.

BET surface area: The BET surface area of the support is generally inthe range 100 m²/g to 500 m²/g, preferably in the range 250 m²/g to 450m²/g, and for silica-alumina based supports, more preferably in therange 310 m²/g to 450 m²/g.

Mean pore diameter: For the preferred catalysts based on silica-alumina,the mean pore diameter of the catalyst is measured from the poredistribution profile obtained using a mercury porosimeter. The mean porediameter is defined as being the diameter corresponding to a zeroderivative of the curve obtained from the mercury porosity curve. Themean pore diameter, as defined, is in the range 1 nm (1×10⁻⁹ meters) to12 nm (12×10⁻⁹ meters), preferably in the range 1 nm (1×10⁻⁹ meters) to11 nm (11×10⁻⁹ meters) and more preferably in the range 3 nm (4×10⁻⁹meters) to 10.5 nm (10.5×10⁻⁹ meters).

Pore distribution: The preferred catalyst for use in the presentinvention has a pore distribution such that the pore volume of the poreswith a diameter in the range from the mean diameter as defined abovereduced by 3 nm and the mean diameter as defined above increased by 3 nm(i.e., the mean diameter ±3 nm) is more than 40% of the total porevolume and preferably in the range 50% to 90% of the total pore volume,more advantageously again between 50% and 70% of the total-pore volume.

Overall pore volume of support: For silica-alumina based supports, it isgenerally less than 1.0 ml/g, preferably in the range 0.3 to 0.9 ml/g,and more advantageously less than 0.85 ml/g.

The support, and in particular the silica-alumina (used in the preferredimplementation) is prepared and formed using the usual methods that arewell known to the skilled person. Advantageously, prior to impregnatingthe metal, the support is calcined, for example by means of a heattreatment at 300-750° C. (preferably 600° C.) 0.25 to 10 hours(preferably 2 hours) in 0-30% by volume of steam (preferably about 7.5%for a silica-alumina matrix).

The metal salt is introduced using one of the usual methods fordepositing a metal (preferably platinum and/or palladium, platinum beingmore preferred) on the surface of a support. One preferred method is dryimpregnation, which consists of introducing the metal salt into a volumeof solution which is equal to the pore volume of the catalyst mass to beimpregnated. Before the reduction operation, the catalyst is calcined,for example in dry air at 300-750° C. (preferably 520° C.) for 0.25-10hours (preferably 2 hours).

Before using the hydroisomerisation-conversion reaction, the metalcontained in the catalyst has to be reduced. One preferred method forreducing the metal is a treatment in hydrogen at a temperature in therange 150° C. to 650° C. and at a total pressure in the range 0.1 to 25MPa. As an example, reduction consists of a constant temperature stageat 150° C. for 2 hours then raising the temperature to 450° C. at a rateof 1° C./min followed by a constant temperature stage of 2 hours at 450°C.; during the whole of this reduction step, the hydrogen flow rate is1000 l of hydrogen/l of catalyst. It should also be noted that anyex-situ reduction method is suitable.

The operating conditions under which step a) is carried out areimportant.

The pressure is generally in the range 2 to 25 MPa (usually at least 5MPa), preferably 2 (or 3) to 20 MPa and advantageously 2 to 18 MPa; thehourly space velocity is normally in the range 0.1 h⁻¹ to 10 h⁻¹,preferably in the range 0.2 to 10 h⁻¹ and advantageously in the range0.1 or 0.5 h⁻¹ to 5.0 ⁻¹, and the hydrogen ratio is advantageously inthe range 100 to 2000 liters of hydrogen per litre of feed andpreferably in the range 150 to 1500 liters of hydrogen per litre offeed.

The temperature used in this step is usually in the range 200° C. to500° C. (or 450° C.) and preferably in the range 250° C. to 450° C.,advantageously in the range 300° C. to 450° C. and more advantageouslymore than 340° C., for example in the range 320-450° C.

The hydrotreatment and hydroisomerisation-conversion steps can becarried out using two types of catalysts in a plurality (two or more) ofdifferent reactors, and/or on at least two catalytic beds installed inthe same reactor.

As demonstrated in U.S. Pat. No. 5 879 539, the use of the catalystbelow described in step a) increases the viscosity index (VI) by +10points. More generally, the increase in VI is at least 2 points, the VIbeing measured on a solvent dewaxed feed (residue) and on the productfrom step a), also solvent dewaxed, aiming at a pour point temperaturein the range −15° C. to −20° C.

In general, the VI is increased by at least 5 points, and usually bymore than 5 points, or even 10 points or more than 10 points.

It is possible to control the increase in VI by measuring theconversion. It is thus possible to optimise the production towards highVI oils or to higher oil yields but with a VI that is not as high.

In parallel to increasing the VI, the pour point is usually reduced,from a few degrees up to 10-15° C. or more (for example 25° C.). Thesize of the reduction varies depending on the conversion and thus on theoperating conditions and the feed.

Treatment of Effluent From Step a)

In a preferred implementation, the whole of the effluent fromhydroisomerisation-conversion step a) is treated in dewaxing step b). Ina variation, at least a portion (and preferably at least the majorportion) of the light gases comprising hydrogen and possiblyhydrocarbon-containing compounds containing at most 4 carbon atoms canbe separated. Hydrogen can be separated first. The implementation (not avariation) with passage of the whole of the effluent from step a) intostep b) is of economic interest since a single distillation unit is usedat the end of the process. Further, the final distillation (aftercatalytic dewaxing or subsequent treatments) produces a low temperaturegas oil.

Advantageously, in a further implementation, the effluent from step a)is distilled to separate the light gases and also to separate at leastone residue containing compounds with a boiling point of more than atleast 340° C. Preferably, atmospheric distillation is carried out.

Advantageously, distillation can be carried out to obtain a plurality offractions (gasoline, kerosine, gas oil, for example) with a boilingpoint of at most 340° C. and a fraction (residue) with an initialboiling point of more than at least 340° C. and preferably more than350° C., more preferably at least 370° C. or 380° C.

In a preferred variation of the invention, this fraction (residue) isthen treated in a catalytic dewaxing step, i.e., without undergoingvacuum distillation. However in a still further variation, vacuumdistillation can be carried out.

In an implementation which is more closely aimed at producing middledistillates, and in accordance with the invention, a portion of theresidue from the separation step can be recycled to the reactorcontaining the conversion-hydroisomerisation catalyst to convert it andincrease the production of middle distillates.

In general, the term “middle distillates” as used in this text isapplied to fraction(s) with an initial boiling point of at least 150° C.and an end point of just before the residue, i.e., generally up to 340°C., 350° C., preferably less than 370° C. or 380° C.

Before or after distillation, the effluent from step a) can undergoother treatments such as extraction of at least a portion of thearomatic compounds.

Step b): Catalytic Hydrodewaxing

At least a portion of the effluent from step a), which effluent haspossibly undergone the separation and/or treatment steps describedabove, then undergoes a catalytic dewaxing step in the presence ofhydrogen and a hydrodewaxing catalyst comprising an acidic function, ametallic hydro-dehydrogenating function and at least one matrix.

It should be noted that compounds boiling above at least 340° C. alwaysundergo catalytic dewaxing.

The Catalyst

The acid function is provided by at least one molecular sieve,preferably a molecular sieve with a microporous system having at leastone principal channel type with openings formed by rings containing 9 or10 T atoms. The T atoms are tetrahedral constituent atoms of themolecular sieve and can be at least one of the elements contained in thefollowing set of atoms: (Si, Al, P, B, Ti, Fe, Ga). Atoms T, definedabove, alternate with an equal number of oxygen atoms in the constituentrings of the channel openings. Thus it can also be said that theopenings are formed from rings containing 9 or 10 oxygen atoms or formedby rings containing 9 or 10 T atoms.

The catalyst of the invention comprises at least one sieve selected fromZBM-30, EU-2 and EU-11. It can also comprise at least one molecularsieve with the above characteristics.

The molecular sieve forming part of the composition of the hydrodewaxingcatalyst can also include other channel types but with openings formedfrom rings containing less than 10 T atoms or oxygen atoms.

The molecular sieve forming part of the preferred catalyst compositionalso has a bridging distance, the distance between two pore openings asdefined above, which is at most 0.75 nm (1 nm=10⁻⁹ m), preferably in therange 0.50 nm to 0.75 nm, more preferably in the range 0.52 nm to 0.73nm; such sieves can produce good catalytic performances in thehydrodewaxing step.

The bridging distance is measured using a molecular modelling tool suchas Hyperchem or Biosym, which enables the surface of the molecularsieves under consideration to be constructed using the ionic radii ofthe elements present in the sieve framework, to measure the bridgingdistance.

The use of molecular sieves selected in this manner and under theconditions described above selected from the numerous molecular sievesalready in existence enables products with a low pour point and a highviscosity index to be produced in good yields in the process of theinvention.

Examples of molecular sieves which can be used in the preferredcomposition of the catalytic hydrodewaxing catalyst are the followingzeolites: ferrierite, NU-10, EU-13, EU-1.

Preferably, the molecular sieves used in the composition of thehydrodewaxing catalyst are included in the set formed by ferrierite andEU-1 zeolite.

In general, the hydrodewaxing catalyst comprises a zeolite selected fromthe group formed by NU-10, EU-1, EU-13, ferrierite, ZSM-22, Theta-1,ZSM-50, ZSM-23, NU-23, ZSM-35, ZSM-48, ISI-1, KZ-2, ISI-4, KZ-1.

The quantity of molecular sieve in the hydrodewaxing catalyst is in therange 1% to 90% by weight, preferably in the range 5% to 90% by weightand more preferably in the range 10% to 85% by weight.

Non limiting examples of matrices used to produce the catalyst arealumina gel, alumina, magnesia, amorphous silica-alumina and mixturesthereof Techniques such as extrusion, pelletisation or bowl granulationcan be used to carry out the forming operation.

The catalyst also comprises a hydro-dehydrogenating function ensured,for example, by at least one group VIII element and preferably at leastone noble element selected from the group formed by platinum andpalladium. The amount of non noble group VIII metal with respect to thefinal catalyst is in the range 1% to 40%, preferably in the range 10% to30%. In this case, the non noble metal is often associated with at leastone group VIB metal (preferably Mo and W). If at least one noble groupVIII metal is used, the quantity with respect to the final catalyst isless than 5% by weight, preferably less than 3% and more preferably lessthan 1.5%.

When using noble group VIII metals, the platinum and/or palladium is/arepreferably localised on the matrix.

The hydrodewaxing catalyst of the invention can also contain 0 to 20%,preferably 0 to 10% by weight (expressed as the oxides) of phosphorus. Acombination of group VIB metal(s) and/or group VIII metal(s) withphosphorus is particularly advantageous.

The Treatment

The residue obtained from step a) and distillation and which is treatedin this hydrodewaxing step b) has the following characteristics: it hasan initial boiling point of more than 340° C. and preferably more than370° C., a pour point of at least 15° C., a viscosity index of 35 to 165(before dewaxing), preferably at least 110 and more preferably less than150, a viscosity at 100° C. of 3 cSt (mm²/s) or more, an aromaticcompound content of 10% by weight, a nitrogen content of less than 10ppm by weight, and a sulphur content of less than 50 ppm by weight or,preferably, 10 ppm by weight.

The operating conditions for the catalytic step of the process of theinvention are as follows:

-   the reaction temperature is in the range 200° C. to 500° C.,    preferably in the range 250° C. to 470° C., advantageously 270-430°    C.;-   the pressure is in the range 0.1 (or 0.2) to 25 MPa (10⁶ Pa),    preferably in the range 1.0 to 20 MPa;-   the hourly space velocity (HSV, expressed as the volume of feed    injected per unit volume of catalyst per hour) is in the range from    about 0.05 to about 50, preferably in the range about 0.1 to about    20 h⁻¹, more preferably in the range 0.2 to 10 h⁻¹.

They are selected to produce the desired pour point.

The feed and catalyst are brought into contact in the presence ofhydrogen. The amount of hydrogen used, expressed in liters of hydrogenper litre of feed, is in the range 50 to about 2000 liters of hydrogenper litre of feed, preferably in the range 100 to 1500 liters ofhydrogen per litre of feed.

Effluent Obtained

The effluent at the outlet from hydrodewaxing step b) is sent to thedistillation train, which preferably integrates atmospheric distillationand vacuum distillation, with the aim of separating the conversionproducts with a boiling point of less than 340° C. and preferably lessthan 370° C. (and including those formed during the catalytichydrodewaxing step), and separating the fraction which constitutes thebase stock and for which the initial boiling point is more than at least340° C. and preferably 370° C. or more.

Further, this vacuum distillation section can separate different gradesof oils.

Preferably, before being distilled, at least a portion and preferablythe whole of the effluent from the outlet from catalytic hydrodewaxingstep b) is sent over a hydrofinishing catalyst in the presence ofhydrogen to carry out deep hydrogenation of the aromatic compounds whichhave a deleterious effect on the stability of the oils and distillates.However, the acidity of the catalyst must be sufficiently weak so as notto lead to the formation of a cracking product with a boiling point ofless than 340° C. so as not to degrade the final yields, in particularthe oil yields.

The catalyst used in this step comprises at least one group VII metaland/or at least one element from group VIB of the periodic table. Thestrong metallic functions: platinum and/or palladium, ornickel-tungsten, nickel-molybdenum combinations, are advantageously usedto carry out deep hydrogenation of the aromatic compounds.

These metals are deposited and dispersed on an amorphous or crystallineoxide type support, such as aluminas, silicas and silica-aluminas.

The hydrofinishing (HDF) catalyst can also contain at least one elementfrom group VIIA of the periodic table. Preferably, these catalystscontain fluorine and/or chlorine.

The metal contents are in the range 10% to 30% in the case of non noblemetals and less than 2%, preferably in the range 0.1% to 1.5%, morepreferably in the range 0.1% to 1.0% in the case of noble metals.

The total quantity of halogen is in the range 0.02% to 30% by weight,advantageously 0.01% to 15%, or 0.01% to 10%, preferably 0.01% to 5%.

Catalysts containing at least one noble group VIII metal (for exampleplatinum) and at least one halogen (chlorine and/or fluorine), acombination of chlorine and fluorine being preferred, can be cited ascatalysts suitable for use in this hydrorefining step, and lead toexcellent performances in particular for the production of medicinaloils.

The following operating conditions are employed for the hydrofinishingstep of the process of the invention:

-   the reaction temperature is in the range 180° C. to 400° C.,    preferably in the range 210° C. to 350° C., advantageously 230-320°    C.;-   the pressure is in the range 0.1 to 25 MPa (10⁶ Pa), preferably in    the range 1.0 to 20 MPa;-   the hourly space velocity (HSV, expressed as the volume of feed    injected per unit volume of catalyst per hour) is in the range from    about 0.05 to about 100, preferably in the range about 0.1 to about    30 h⁻¹.

Contact between the feed and the catalyst is carried out in the presenceof hydrogen. The amount of hydrogen used and expressed in liters ofhydrogen per litre of feed is in the range 50 to about 2000 liters ofhydrogen per litre of feed, preferably in the range 100 to 1500 litersof hydrogen per litre of feed.

Advantageously, the temperature of the HDF step is lower than thetemperature of the catalytic hydrodewaxing step (CHDW). The differenceT_(CHDW)-T_(HDF) is generally in the range 20° C. to 200° C., preferablyin the range 30° C. to 100° C. The effluent at the outlet from the HDFstep is sent to the distillation train.

The Products

The base stock obtained using this process has a pour point of less than−10° C., a VI of more than 95, preferably more than 110 and morepreferably more than 120, a viscosity of at least 3.0 cSt at 100° C., anASTM colour of less than 1 and a UV stability such that the increase inthe ASTM colour is in the range 0 to 4, preferably in the range 0.5 to2.5.

The UV stability test, adapted from the ASTM D925-55 and D1148-55procedures, is a rapid method for comparing the stability of lubricatingoils exposed to a source of ultraviolet radiation. The test chamber isconstituted by a metal chamber provided with a rotary plate whichreceives the oil samples. A bulb producing the same ultravioletradiation as that of solar radiation placed in the top of the testchamber is directed downwards onto the samples. The samples include astandard oil with known UV characteristics. The ASTM D1500 colour of thesamples is determined at t=0 then after 45 h of exposure at 55° C. Theresults for the standard sample and the test samples are transcribed asfollows:

a) initial ASTM D1500 colour;

b) final ASTM D1500 colour;

c) increase in colour;

d) cloudiness;

e) precipitate.

A further advantage of the process of the invention is that it ispossible to achieve very low aromatic compound contents of less than 2%by weight, preferably 1% by weight and more preferably less than 0.05%by weight) and even of producing medicinal quality white oils witharomatic compound contents of less than 0.01% by weight. The UVabsorbance values of these oils at 275, 295 and 300 nanometers are lessthan 0.8, 0.4 and 0.3 respectively (ASTM D2008 method) and have aSaybolt colour in the range 0 to 30.

The fact that the process of the invention can also produce medicinalquality white oils is of particular interest. Medicinal white oils aremineral oils obtained by deep refining of petroleum; their quality issubject to different regulations which are aimed at guaranteeing thatthey are harmless for pharmaceutical applications. They are non toxicand are characterized by their density and viscosity. Medicinal whiteoils essentially comprise saturated hydrocarbons, they are chemicallyinert and they have a low aromatic hydrocarbon content. Particularattention is paid to aromatic compounds in particular those containing 6polycyclic aromatic hydrocarbons (PAH) which are toxic and present inconcentrations of one part per million by weight of aromatic compoundsin white oil. The total aromatic content can be monitored using the ASTMD2008 method, this UV absorption test at 275, 292 and 300 nanometersenabling an absorbance of less than 0.8, 0.4 and 0.3 respectively to bemonitored (i.e., the white oils have aromatic compound contents of lessthan 0.01% by weight). These measurements are made with concentrationsof 1 g of oil per litre, in a 1 cm cell. Commercially available whiteoils are distinguished by their viscosity and also by their crude oforigin which may be paraffinic or naphthenic, these two parameterscausing differences both in the physico-chemical properties of the whiteoils and in their chemical composition.

Currently, oil cuts whether originating from straight run distillationof a crude petroleum followed by extraction of aromatic compounds by asolvent, or from a catalytic hydrorefining or hydrocracking process,still contain non negligible quantities of aromatic compounds. Currentlegislation in the majority of industrialised nations requires thatmedicinal white oils must have an aromatic compound content below athreshold imposed by the legislation in each of the countries. Theabsence of these aromatic compounds in oil cuts results in a Sayboltcolour specification which must be substantially at least 30 (+30), amaximum UV adsorption which must be less than 1.60 at 275 nm on a pureproduct in a 1 centimeter cell and a maximum absorption specificationfor products extracted by DMSO which must be less than 0.1 for theAmerican market (Food and Drug Administration, standard n° 1211145).This latter test consists of specifically extracting polycyclic aromatichydrocarbons using a polar solvent, usually DMSO, and checking theircontent in the extract by measuring the UV absorption in the 260-350 nmrange.

The invention will now be illustrated using FIGS. 1 to 3, representingdifferent implementations for the treatment of a feed from theFischer-Tropsch process or of a hydrocracking residue, for example.

FIG. 1

In FIG. 1, the feed enters via a line (1) into a hydrotreatment zone (2)(which can be composed of one or more reactors, and comprises one ormore catalytic beds of one or more catalysts) into which the hydrogenenters (for example via line (3)) and where the hydrotreatment step iscarried out.

The hydrotreated feed is transferred via line (4) into ahydroisomerisation zone (7) (which can be composed of one or morereactors, and comprises one or more catalytic beds of one or morecatalysts) where hydroisomerisation step a) is carried out in thepresence of hydrogen. Hydrogen can be supplied via a line (8).

In this figure, before being introduced into zone (7), the feed to behydroisomerised is freed of a large portion of its water in drum (5),the water leaving via line (6) and possibly ammonia and hydrogensulphide H₂S, when the feed entering via line 1 contains sulphur andnitrogen.

The effluent leaving zone (7) is sent via a line (9) to a drum (10) toseparate hydrogen via a line (11); the effluent is then distilled underatmospheric pressure in a column (12) from which a light fractioncomprising compounds containing at most 4 carbon atoms and those boilingbelow this are extracted overhead via a line (13).

At least one gasoline fraction (14) and at least one middle distillate(kerosine (15) and gas oil (16), for example) are obtained.

A fraction containing compounds with a boiling point of more than atleast 340° C. is obtained from the bottom of the column. This fractionis evacuated via line (17) to catalytic dewaxing zone (18).

Catalytic dewaxing zone (18) (comprising one or more reactors, one ormore catalytic beds of one or more catalysts) also receives hydrogen viaa line (19) to carry out step b) of the process.

The effluent leaving via line (20) is separated in a distillation traincomprising, in addition to drum (21) for separating hydrogen via a line(22), an atmospheric distillation column (23) and a vacuum column (24)which treats the atmospheric distillation column transferred via line(25), the residue having an initial boiling point of more than 340° C.

The products from the distillations are an oil fraction (line 26), andlower boiling fractions such as gas oil (line 27), kerosine (line 28),gasoline (line 29); light gases are eliminated via line (30) of theatmospheric column and via line (31) of the vacuum distillation column.

The effluent leaving via line (20) can advantageously be sent to ahydrofinishing zone (not shown) (comprising one or more reactors, one ormore catalytic beds of one or more catalysts) before being injected intothe separation train. Hydrogen can be added to this zone if necessary.The departing effluent is then transferred to drum (21) and thedistillation train described above.

In order not to complicate the figure, the hydrogen recycle has not beenshown, either from drum (10) to the hydrotreatment and/orhydroisomerisation step, and/or from drum (21) to the dewaxing and/orhydrofinishing step.

FIG. 2

This uses the reference numerals of FIG. 1. In this implementation, thewhole of the effluent from hydroisomerisation-conversion zone (7) (stepa)) passes directly via line (9) into catalytic dewaxing zone (18) (stepb)).

FIG. 3

This also uses the reference numerals of FIG. 1. In this implementation,the effluent from the hydroisomerisation-conversion zone (7) (step a)undergoes separation in drum (32) of at least a portion of the lightgases (hydrogen and hydrocarbon-containing compounds containing at most4 carbon atoms), for example by flashing. The separated gases areextracted via line (33) and the residual effluent is sent via line (34)into catalytic dewaxing zone (18).

It should be noted that in FIGS. 1, 2 and 3, the effluent from catalyticdewaxing zone (18) is separated. This separation need not be carried outwhen said effluent is subsequently treated in a hydrofinishing zone, asseparation then takes place after that treatment.

This concerns separation carried out in drums or columns 21, 23, 24.

1. A process for producing oils having an improved pour point andviscosity index from a hydrocarbon feed, said process comprising thefollowing steps in succession: (a) converting the feed with simultaneoushydroisomerisation of at least a portion of the n-paraffins of the feed,said feed having a sulphur content of less than 1000 ppm by weight, anitrogen content of less than 200 ppm by weight, a metals content ofless than 50 ppm by weight, an oxygen content of at most 0.2% by weight,said step being carried out at a temperature of 200-500° C., at apressure of 2-25 MPa, with a space velocity of 0.1-10 h⁻¹, in thepresence of hydrogen, and in the presence of a catalyst containing atleast one noble metal deposited on an amorphous acidic support, thedispersion of the noble metal being 20-100%; (b) catalytic dewaxing ofat least a portion of the effluent from step a), carried out at atemperature of 200-500° C., at a pressure of 1-25 MPa, with an hourlyspace velocity of 0.05-50 h⁻¹, in the presence of 50-2000 litres ofhydrogen/litre of effluent entering step b)), and in the presence of acatalyst comprising at least one hydrodehydrogenating element and atleast one molecular sieve selected from ZBM-30, EU-2 and EU-11 zeolites.2. A process according to claim 1, in which a catalyst containing atleast one noble metal deposited on an amorphous silica-alumina isemployed in step a).
 3. A process according to claim 1, in which in stepa), a catalyst is used that is essentially constituted by 0.05-10% byweight of at least one noble group VIII metal deposited on an amorphoussilica-alumina support containing 5-90% by weight of silica, with a BETspecific surface area of 100-500 m²/g and the catalyst has: a mean porediameter in the range 1-12 nm; a pore volume of pores with a diameter inthe range between the mean diameter as hereinbefore defined reduced by 3nm and the mean diameter as hereinbefore defined increased by 3 nm ismore than 40% of the total pore volume; a noble metal dispersion in therange 20%-100%; a coefficient of distribution of the noble metal of morethan 0.1.
 4. A process according to claim 1, in which the noble metal inthe catalyst for step a) is platinum and/or palladium.
 5. A processaccording to claim 1, in which all of the effluent from step a) istreated in step b).
 6. A process according to claim 1, in which theeffluent from step a) is distilled to separate the light gases and atleast one residue containing compounds with a boiling point of more thanat least 340° C., said residue undergoing step b).
 7. A processaccording to claim 1, in which the effluent from step b) is distilled toseparate an oil containing compounds with a boiling point of more thanat least 340° C.
 8. A process according to claim 7, comprisingatmospheric distillation followed by vacuum distillation of theatmospheric residue.
 9. A process according to claim 1, in which thefeed undergoing step a) previously undergoes hydrotreatment thenoptional separation of water, ammonia and hydrogen sulphide.
 10. Aprocess according to claim 1, in which the catalytic dewaxing catalystalso contains at least one zeolite selected from NU-10, EU-1, EU-13,ferrierite, ZSM-22, Theta-1, ZSM-50, ZSM-23, NU-23, ZSM-35, ZSM-38,ZSM-48, ISI-1, KZ-2, ISI-4, and KZ-1.
 11. A process according to claim1, in which the effluent from step b) undergoes a hydrofinishing stepbefore being distilled.
 12. A process according to claim 1, in which thetreated hydrocarbon feed contains at least 20% by volume of compoundswith boiling points above 340° C.
 13. A process according to claim 1, inwhich the treated hydrocarbon feed is selected from effluents from aFischer-Tropsch unit, vacuum distillates from straight run distillationof crude oil, vacuum distillates from conversion units, vacuumdistillates from aromatic compound extraction units, vacuum distillatesoriginating from desulphurisation or hydroconversion of atmosphericresidues and/or vacuum residues, deasphalted oils, hydrocrackingresidues or any mixture of said feeds.
 14. A catalyst comprising atleast one molecular sieve selected from ZBM-30, EU-2, and EU-11, and atleast one other molecular sieve the microporous system of which has atleast one principal channel type with openings formed from ringscontaining 10 or 9 tetrahedral T atoms, T being at least one of elementsSi, Al, P, B, Ti, Fe, Ga.
 15. A catalyst according to claim 14, in whichsaid at least one other molecular sieve is selected from NU-10, EU-1,EU-13, ferrierite, ZSM-22, Theta-1, ZSM-50, ZSM-23, NU-23, ZSM-35,ZSM-38, ZSM-48, 151-1, KZ-2, ISI-4, and KZ-1.
 16. A catalyst accordingto claim 14, in which the amount of the molecular sieve is 1-90% byweight.
 17. A catalyst according to claim 14, further comprising amatrix.
 18. A catalyst according to claim 17, in which the matrix isselected from the group formed by alumina gels, aluminas, magnesia,amorphous silica-alumina and mixtures thereof.
 19. A catalyst accordingto claim 14, in which the hydrodehydrogenating function is provided byat least one element from group VIII.
 20. A catalyst according to claim19, in which the element is platinum and/or palladium.
 21. A catalystaccording to claim 19, in which the hydrodehydrogenating function isprovided by 1-40% by weight of at least one non-noble metal from groupVIII and at least one metal from group VIB.
 22. A catalyst according toclaim 19, containing 0-20% (by weight of oxide) of phosphorus.
 23. Acatalytic hydrodewaxing process according to claim 1 wherein said atleast one molecular sieve comprises ZBM
 30. 24. A catalytichydrodewaxing process according to claim 1 wherein said dispersion ofthe noble metal is 30-100%.
 25. A catalytic hydrodewaxing processaccording to claim 23 wherein said dispersion of the noble metal is30-100%.
 26. A catalytic hydrodewaxing process according to claim 25wherein the noble metal catalyst comprises platinum.
 27. A catalytichydrodewaxing process according to claim 10 wherein said dispersion ofthe noble metal is 30-100%.
 28. A catalyst according to claim 15comprising ZBM-30.